The frequency, aetiology and outcome of severe hyponatraemia in adult hospitalised patients.

OBJECTIVE

To study the frequency, outcome and association with neurological signs and symptoms of severe hyponatraemia (< 120 mmol/l) in adult hospitalised patients.

DESIGN

Retrospective study of severe hyponatraemia using laboratory data to identify patients.

SETTING

800 bed peri-urban hospital in the former homeland of Transkei.

SUBJECTS

All adult inpatients from the medical and surgical wards with severe hyponatraemia during a 10 month period of which 18 cases records could not be traced and one was antefactual.

MAIN OUTCOME MEASURES

Incidence of severe hyponatraemia, mortality, admission hyponatraemia, hospital acquired hyponatraemia, neurological symptoms and outcome.

RESULTS

The overall incidence of severe hyponatraemia was 1.1%. Among the 58 patients (mean age 49.3 years), pulmonary tuberculosis (24%), Diabetes mellitus (19%) and renal failure (17.2%) were the principal aetiological conditions occurring in approximately 60% of hyponatraemic patients. A high mortality rate of 44.8% was observed which was probably associated with the severity of the underlying disease. 36.2% of patients had serum sodium levels of less than 115 mmol/l with a significantly (p < 0.05) higher mortality (62%) than those with values greater than 115 mmol/l (32%). Admission hyponatraemia (63.8%) was more frequent (p < 0.05) than hospital acquired hyponatraemia (36.2%); in the latter, hyponatraemia was more likely to normalise (p < 0.05). Neurological signs and symptoms developed in 17.2%, this being associated with a high mortality and lower mean serum sodium levels of 112 mmol/l respectively. Following therapy, serum sodium levels normalised in nearly half the patients. In three (5.2%) patients, the hyponatraemia worsened whilst another three became hypernatraemic.

CONCLUSION

The incidence of severe hyponatraemia was lower than that observed in developed countries. It was associated with severe underlying disease and had a high mortality rate. Patients whose hyponatraemia did not normalise were more likely to have higher mortality.